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Official PYQ · 2012Q23Fragmentation and IP Addressing, IPv4, CIDRMCQ1 mark

GATE CS 2012 Q23 — Fragmentation and IP Addressing, IPv4, CIDR

Explain with AI

In the IPv4 addressing format, the number of networks allowed under Class CC addresses is:

Choose one option
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Answer: C

In classful IPv4 addressing, IP addresses are divided into five classes (A, B, C, D, and E). For Class C addresses:

  • The first octet starts with the fixed binary prefix 110 (3 bits).
  • The network ID portion occupies the first 24 bits (3 octets).
  • The remaining 8 bits (1 octet) are used for the host ID.

Since the first 3 bits of the 24-bit network ID are fixed as 110, the number of variable bits available to uniquely identify Class C networks is:

Network bits=24−3=21 bits\text{Network bits} = 24 - 3 = 21 \text{ bits}

Therefore, the total number of allowed Class C networks is:

2212^{21}

Hence, the correct option is C.

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